Design of modules of a display device adopting Active Matrix/Organic Light Emitting Diode (AMOLED) is quite complicated, and when a resolution of the display device is increased to more than 3840×2160 (large-size display), a design of four sub-pixels with different colors (that is, Red, Green, Blue and White, RGBW for short) is generally adopted. For the design of four sub-pixels with different colors, a gate/source double-driving method is generally used. FIG. 1 shows a schematic diagram of a driving circuit for four sub-pixels with different colors in the prior art, as shown in FIG. 1, the pixel driving circuit in the prior art comprises: a first driving circuit board, a second driving circuit board and a pixel array, wherein the first driving circuit board comprises several first sub-pixel driving chips 201, the second driving circuit board comprises several second sub-pixel driving chips 301, and the pixel array comprises several pixels. Furthermore, each pixel comprises a red sub-pixel 101, a green sub-pixel 102, a blue sub-pixel 103 and a white sub-pixel 104, wherein one first sub-pixel driving chip and one second sub-pixel driving chip are provided corresponding to several pixels, that is, each of the first sub-pixel driving chips is connected to all of the red sub-pixel, the green sub-pixel, the blue sub-pixel and the white sub-pixel of a pixel corresponding thereto, and each of the second sub-pixel driving chips is connected to all of the red sub-pixel, the green sub-pixel, the blue sub-pixel and the white sub-pixel of a pixel corresponding thereto, each sub-pixel is connected to a pin of a pixel driving chip corresponding thereto. In general, the first sub-pixel driving chip and the second sub-pixel driving chip refer to X-direction circuit boards and are provided at upper portion or lower portion of the display panel of the display device respectively.
Each of the sub-pixel driving chips comprises four set of DA converters, which correspond to the above-mentioned four sub-pixels with different colors, that is to say, each set of DA converters correspond to sub-pixels of one color and correspond to one set of Gamma voltage supplies, each set of Gamma voltage supplies occupies 9, 8 or 7 pins of the sub-pixel driving chip. Taking one set of Gamma voltage supplies occupying 9 pins as an example, four sets of Gamma voltage supplies for one pixel occupy 36 pins. Since signal lines for Gamma voltage supplies are exposed outside, large number of Gamma voltage supplies may result in large amount of noise, which may affect the display quality. In addition, the sub-pixel driving chip is expensive in cost, use of its pins should be saved as far as possible. Also, the pixel driving circuit in the prior art will use a large number of sub-pixel driving chips to satisfy requirements on pins, thus too many devices may result in a large-sized display device, and it is difficult to meet the requirements on thin and compact design of display device.